10-5-7: STORM DRAINAGE:
   A.   Design: Streets, blocks, depths of lots, parks and other public grounds shall be located and laid out in such a manner as to preserve and utilize natural streams, channels and detention basins, including, wherever possible, the latter within parks or other public grounds.
   B.   Channel Straightening: Sharply meandering streams or channels may be partly straightened and minor changes made in other channels, subject to approval of the Village Engineer, provided:
      1.   The floodway dimensions of the stream or channel are maintained.
      2.   The volume of flood water storage outside the floodway is not reduced.
   C.   Uppermost Reaches of Drainage Channels: Poorly defined drainage channels or swales forming the natural drainage system may be located or eliminated and incorporated into the planned system of storm sewers upon a showing that the system is adequate and can safely handle the flood water runoff following the design rainstorms.
   D.   Ditch and Storm Sewers: Ditch and storm sewers shall be so designed that when the receiving stream is at full flood stage, the ditch or storm sewer will continue to drain the area it is designed to serve. All storm sewers shall be designed using the hydraulic gradient to determine capacity.
   E.   Flood Plain Lots: The subdivider shall comply with the rules and regulations as established by the Village and the Illinois Department of Transportation regarding the Flood Plan. 1
   F.   Street Pavements Near Streams: The crown of street pavements built adjoining or near streams, floodwater runoff channels or detention basins shall not be lower than the established one hundred (100) year high-water elevation.
   G.   Adequate provisions shall be made in all subdivisions for proper drainage of storm water.
      Storm discharges shall be into a storm sewer or ditch system which shall carry the storm water to retention areas approved by the Village.
   H.   The rational method (Q = CIA) shall be employed when computing storm water runoff. The minimum of coefficient or runoff for various types of developments shall be:
 
Single-family and townhouse areas
0.35 - 0.50
Parks
0.15 - 0.40
Lots in excess of 1/2 acre
0.20 - 0.35
Commercial and industrial areas
0.50 - 0.85
 
   The intensity "i", for design purposes, shall be based on a ten (10) year storm frequency for storm sewers and a one hundred (100) year storm frequency for ditches and a duration equal to the time of concentration at the various points of design.
   I.   If curb and gutters are provided, curb drainage structures shall be located at all low points and at other locations as required by the street gradient and area to be served. In no case shall water flowing in curbs exceed four hundred feet (400').
      The maximum allowable width of street gutter flow for the design storm is eight feet (8') measured from the curb face.
   J.   Storm water runoff from subdivided land shall be restricted to no greater than that from its natural or undeveloped state (maximum 3-year frequency with runoff coefficient 0.15) and detention space provided for the excess water, except as provided below:
      A combination of storage and controlled release of storm water runoff is required for all industrial and commercial subdivisions exceeding two (2) acres in area; for all residential subdivisions exceeding ten (10) acres in area; and for all residential subdivisions between two (2) and ten (10) acres which have an imperviousness of sixty percent (60%) or greater. However, exempted areas must have an adequate outlet and prove that their runoff will not damage downstream areas. If the outlet is determined to be inadequate, detention will be required. The release rate shall not exceed the storm water runoff from the area in its natural undeveloped state nor be greater than that calculated from a storm of three (3) year frequency with a runoff coefficient of 0.15, unless the subdivider can show by his detailed calculations, which are acceptable to the Village Engineer, that the receiving stream can accept a greater discharge rate.
   K.   Detention storage will be calculated on the basis of a one hundred (100) year frequency rainfall for the area. The detention volume required will be equal to the runoff for a one hundred (100) year frequency rainfall, for any and all durations, for the subdivision under consideration, less the volume discharged during the same duration at the allowable release rate.
      Drainage systems shall have adequate capacity to bypass through the development the flow from all upstream areas for a storm of ten (10) year design frequency assuming that the land is in a fully developed state under present zoning or zoning proposed under a Village-approved Comprehensive Plan. The bypass flow rate shall be computed utilizing a runoff coefficient of 0.35. Allowances will be made for upstream detention when such upstream detention and release rate has previously been approved by the Village.
   L.   Detention Basin: Dams constructed to form floodwater detention ponds, basins or lakes shall be designed to provide a temporary floodwater storage pool with a minimum of twelve inches (12") of free-board at design high water and shall be provided with outlets which may be set or regulated to detain and empty slowly the storage pool following periods of runoff according to the criteria as established in this Title.
      Wet bottom detention areas which do not have a continuous fresh water flow shall be aerated by mechanical means. Wet bottom detention areas shall have a minimum static water depth of five feet (5').
      Dry bottom detention basins shall be designed to drain within twenty four (24) hours, and shall be sodded and graded to a one percent (1.0%) minimum slope.
   M.   All ditch and storm sewer, drainage structures, and storm water detention design data shall be submitted with the plans and specifications of the subdivision for review by the Village Engineer prior to approval by the Village.
   N.   Pipe materials for use in storm sewers shall be reinforced concrete pipe of the appropriate class with rubber ring or bituminous compound joint in accordance with the Standard Specifications for Road and Bridge Construction, State of Illinois. Materials permitted for pipe culverts shall be reinforced concrete pipe or bituminous coated corrugated metal pipe of the appropriate class or gauge respectively in accordance with the Standard Specifications for Road and Bridge Construction, State of Illinois.
   O.   Catch Basins And Inlets: Catch basins and inlets shall be constructed in accordance with the Village standards. Inlets shall not be used except at locations approved by the Village Engineer.
   P.   Permits Required: No work shall be undertaken until a permit has been received from the Illinois Department of Transportation, Division of Waterways for all work under the jurisdiction of that agency.
   Q.   Design Capacity: Where the storm sewer system to be installed is to serve an area larger than the subdivision, it shall be designed and installed large enough to serve the entire service area. (Ord. 272, 3-20-1978)

 

Notes

1
1. See Section 9-2-2 of this Code.